1. Technical Field
The present invention relates to a method and apparatus for breast self-palpation and detecting changes of mechanical properties in the breast tissue that are indicative of breast cancer and other breast pathologies accompanied by changes in tissue viscoelasticity.
2. Description of the Related Art
Breast Cancer is a major source of cancer morbidity and mortality in women. Currently, the most widely used clinical diagnostic method is mammography. Efforts to reduce mortality via screening mammography have been successful with definite improvement in survival, particularly in women over 50 years old.
An alternative methodxe2x80x94Breast Self-Examination (BSE) is the most common method of breast cancer detection. About two-thirds of cancers are detected by palpation. Such sensitivity of BSE is related to significant changes in mechanical properties of tissues in the course of breast cancer development. The BSE is widely advised and taught to women as a means of pre-clinical testing and contributes significantly to early cancer detection. A major fraction of breast cancer is first detected by women themselves, who bring the problem to the attention of their physicians. The usefulness of palpatory self-examination as a pre-clinical test is well proven by a wealth of data. The major drawback of this method is that only large size nodules are detectable by palpation. An average examiner, including women conducting breast self-examinations, does not reliably detect lesions until they approach 2 cm in diameter, which may represent a significantly advanced stage of cancer. Even a highly experienced examiner is able to detect a nodule only over 1 cm in diameter, which still may correspond to a considerably advanced cancer.
It is apparent, therefore, that further investigation into screening techniques with greater sensitivity is urgently warranted. Availability of an easy to use, hand-held device for a regular home testing will facilitate regular self-examinations conducted by women and lead to vast improvement in lowering the morbidity and mortality of breast cancer.
There have been many attempts to develop methods and devices for sensing the regions of hardening in tissues and thus, mimicking manual palpation aimed to detect breast cancer. Several authors have proposed various devices for breast palpation using different types of force sensors but all with limited success. For example, proposals by Gentle (Gentle C R, xe2x80x9cMammobarography: a possible method of mass breast screeningxe2x80x9d, J. Biomed. Eng. 10, 124-126, 1988) was capable of detecting lumps of 6 mm in diameter in breast phantoms but was unable to obtain any quantitative data on lumps in a real breast. Many of the proposed BSE means were related to simple non-computerized mechanical systems enhancing sense of touch such as apparatuses described in U.S. Pat. No. 5,572,995, U.S. Pat. No. 4,657,021, U.S. Pat. No. 4,793,354, and U.S. Pat. No. D348,618 Various types of devices mimicking palpation to detect tumors using different types of force sensors have been suggested. For example, Frei et al., U.S. Pat. No. 4,250,894, have proposed an instrument for breast examination that uses a plurality of spaced piezoelectric strips which are pressed into the body being examined by a pressure member which applies a given periodic or steady stress to the tissue beneath the strips.
Another method and devices for breast self-examination is described in U.S. Pat. No. 5,833,634 and U.S. Pat. No. 5,989,199. The sensors used in those devices are based on a force sensor array manufactured by Tekscan Inc., Boston, Mass. The array consists of conductive rows and columns whose intersecting points form sensing locations. The rows and columns are separated by a material, which changes its electrical resistance under applied force, and thus each intersection becomes a force sensor.
The present invention, Self-Palpation Device (SPD), utilizes the same mechanical information as obtained by manual palpation conducted by a skilled physician but objectively and with higher sensitivity and accuracy. The proposed method and device provides detection of tissue heterogeneity and hard inclusions by measuring changes in the surface stress pattern using a force sensing array applied to the tissue in the oscillatory mode. Temporal and spatial changes of the spectral components and phase relationships of oscillatory signals from the sensors contain information on the mechanical properties and geometry of the internal structures of the breast.
The method and devices in accordance with the present invention enable the user to detect changes in the breast tissue that could be indicative of cancer development. The apparatus of the current invention uses sensors based on piezopolymer PVDF films and comprises mechanical arrangements allowing to increase PVDF signal while providing a good spatial resolution. PVDF film provides inexpensive means for measuring mechanical forces by converting them into an electrical signal. The apparatus also comprises a data acquisition circuit, and a microprocessor that are mounted in a hand held pad. Detection of nodules is achieved by analyzing the dynamic and spatial features of the measured signals obtained by pressing the probe to the breast and oscillating it over the area under investigation. The device is able to objectively detect the mechanical changes in a breast that could be an indication of cancer development.
The present invention provides indications on how elasticity differences in localized areas inside of tissue and respective changes in the spectral components as well as temporal and spatial derivatives of the oscillatory signals from the force sensors on the surface of the tissue are inter-related. The present invention also determines how the above relationship can be used for forming the basis for a method of detecting and quantifying tissue abnormalities.
A significant new feature of SPD is its learning ability needed for developing individually optimized diagnostic criteria. Learning algorithms implemented in the software of SPD make it possible to significantly increase the sensitivity of SPD by fine tuning the device to specific anatomical and physiologic features of a particular woman.
The learning ability of a home-use medical diagnostic system, such as the breast Self-Palpation Device of the present invention, is based on the fact that the data collected during an extended period of time provides means for defining much more precisely the xe2x80x9cnormal statexe2x80x9d of a particular organ and thus, detecting meaningful deviations from the normal state with greater sensitivity.
Medical logic for diagnosis is typically based on the principle that healthy state of body is an objective notion and should be defined by xe2x80x9cnormalxe2x80x9d intervals for vital parameters, which are the same for all people. For instance, if there are no palpable nodules in a breast, it is considered appropriate to qualify that breast xe2x80x9cnormalxe2x80x9d from a mechanical point of view. At the same time, a particular, seemingly xe2x80x9cnormalxe2x80x9d, breast could have detectable mechanical changes resulting from a cancer development, but these changes are within the range of statistical variation of properties of the breast in general. Such meaningful changes can be detected only if one relates these changes to an individual baseline of a particular patient. The proposed self-palpation device of the present invention is based on a principle of medical diagnosis, by which the ranges of parameters that define the healthy state are determined individually.
Every human body is a complex dynamic system with a high level of self-adapting mechanisms. The term xe2x80x9cnormal rangexe2x80x9d for a parameter of an organism should be linked to its specific environment. In other words, while in one condition a particular range is normal, in another, the same range corresponds to an abnormality in the body.
The principle of individual normality can be described by using a formal model of a diagnostic process in general. A vector space A of xe2x80x9cvital statesxe2x80x9d of an organ or entire organism can be considered. A single point (a vector a={a1, a2, . . . , ak} of the space) represents xe2x80x9can elementary temporalxe2x80x9d state for a given organ or organism. The elementary state is defined by a set of vital parameters measured over a particular short period of time. Accordingly, the biological life of the investigated organism can be represented as a sequence of elementary states S= less than s1, s2, . . . , sN greater than  based on the sequence of the periods T={1,2, . . . , N}. Every element from the sequence is a point in A, and the sequence S can be interpreted as a trajectory of xe2x80x9celementaryxe2x80x9d transformations Ts(i)=s(i+1). The main idea to introduce xe2x80x9cindividual standardxe2x80x9d for xe2x80x9cnormalxe2x80x9d and xe2x80x9cabnormalxe2x80x9d states is based on the well known fact that if a clinician looks at a single element s(i) from S, he/she often cannot estimate the normality of the state, but if he/she can observe the entire sequence S the estimation of s(i) is not a hard problem in the most of cases.
The sequence S can be presented by an average state s*(S). Variance v(s*) of the average is a simplest measure of uncertainties of how well s* represents S. If v(s*) is small enough the representation gives a good approximation for S. This state will be referred to as xe2x80x9cstable temporally and individuallyxe2x80x9d because of its stability during a long period of life time. If the variance for every vital parameters is small during period T and the average value for each of them belongs to xe2x80x9cobjectivexe2x80x9d intervals of norms the s*(S) as will be referred to as xe2x80x9cnormalxe2x80x9d for a given patient for the period of time T. Otherwise, the state of S will be referred to as xe2x80x9cabnormalxe2x80x9d.
In the extended sequence of elementary states Sxe2x80x2={S, s(N+1)}, the elementary state s(N+1) is called xe2x80x9calarm-statexe2x80x9d if the state of S is normal while the state of Sxe2x80x2 is abnormal.
The principle of xe2x80x9cindividual normalityxe2x80x9d of the breast proposed in the present invention is based on a predefined choice of concrete values for several parameters (such as N, thresholds on variances for all vital parameters, etc.). The list of parameters which can be considered xe2x80x9crelevantxe2x80x9d and can be used as state characteristics need to be predefined.
In general, there are many approaches to represent a set by its members. For example, one can use a simple average representation. Other approaches, such as median representatives, can also be used.